Shaped charge perforating apparatus



April 14, 1964 FIG.3

LINER THICKNESS (PERCENT OF LINER DIAMETER) April 14, 1964 Filed July24, 1958 J. s. RINEHART ETAL SHAPED CHARGE PERFORATING APPARATUS 2Sheets-Sheet 2 FIG.4

SPECIFIC I GRAVITY OF LINER METAL OR ALLOY United States Patent Ofilice3,128,701 SHAPED CHARGE PERFORATING APPARATUS John S. Rinehart,Cambridge, Mass., and Robert D. Cocanower, Dallas, Tex., assignors toThe Western Company of North America, a corporation of Delaware FiiedJuly 24, 1958, Ser. No. 750,657 3 Claims. (Cl. 102-20) This inventionrelates to an improved device for perforating oil well casings and wellbore holes. More particularly, the invention relates to an explosive jetcharge which is capable of efiectively perforating an oil well casingwithout leaving a slug or carrot of metal in the resulting hole tothereby obstruct the flow of oil or gas into the perforation.

Shaped charges, capable of producing an explosive jet, have beenemployed in recent years to perforate oil Well bore hole casings. Ingeneral, these charges have been characterized by a shaped explosivecharge housed in a container having one open end at which the explosiveprovides a concave surface facing the casing at the point to beperforated. This concave surface is normally lined with a metallic linerwhich seals off the open end of the charge container. This metallicliner has been made conventionally of copper or steel or other highmelting metal or alloy. Such liners have been reasonably suitable foroil well operations except for one serious drawback. Liners of copperand steel and other such high melting metals are prone to leave a metalplug or carrot in the hole formed in the earth by the explosive jet.This plug or carrot usually lodges about one-third of the Way into thehole made by the jet and substantially blocks oif the other two-thirdsof the hole. This means that as much as two-thirds of the possible oilorgas producing area penetrated by the jet is obstructed and the flow ofoil or gas from this area is prevented. This phenomenon is such a commonoccurrence that carroting has been considered by the oil recoveryindustry to be inherent in the use of shaped charges.

It is accordingly an object of the present invention to provide animproved apparatus for perforating the casing of an oil well borehole.

It is another object of the invention to provide an apparatus capable ofperforating an oil well borehole casing Without producing a metallicslug or carrot in the hole formed in the surrounding earth formation.

It is also an object of the present invention to provide a shapedexplosive charge liner which does not produce a slug or carrot in thepenetrated earth formation.

It is an additional object of the invention to provide a novel processof perforating oil well borehole casings employing the novel apparatusand liner of the invention.

The above enumerated objects, as well as other objects, together withthe advantages of the invention, will be readily comprehended by personsskilled in the art upon reference to the present description, taken inconjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a longitudinal cross-section of one preferred form of theapparatus of the invention showing the parts;

FIGURE 2 is a cross-section of a hole produced in the earth formationsurrounding a well borehole casing by a prior art device employing ashaped charge concave liner of copper or steel, with the hole partiallyblocked by the inherent carrot which frequently forms;

.50-50 mixtures, is also quite suitable.

3,128,701 Patented Apr. 14, 1964 FIGURE 3 is a cross-section of a holeproduced in the earth formation surrounding a well borehole casing by anapparatus in accordance with the present invention without the formationof a slug or carrot of metal from the shaped charge liner; and

FIGURE 4 is a diagram showing the desired relationship of linerthickness to density of the metal composing the liner in the device ofthe present invention.

The objects of the present invention are accomplished by employing aconcave charge liner, such as that shown by 15 in FIG. 1 of thedrawings, which is composed of a metal or alloy capable of melting orbeing substantially completely liquefied at the temperature produced bythe compression resulting from the detonation of the explosive charge.The discovery that a liner composed of a metal or alloy which will meltat temperatures reached upon detonation will not produce a slug orcarrot, constitutes an essential feature of the invention. This featureof the invention will be characterized and explained in greater detailhereinbelow.

In order to describe the apparatus and concave liner of the inventionmore clearly, reference is made to FIG. 1 of the accompanying drawingsillustrating one preferred embodiment of the apparatus of the invention.This is done by way of illustration only and is not to be regarded inany way as a limitation in the scope of the invention. FIG. 1illustrates a longitudinal crossection of a shaped explosive jet chargegun 10. The gun comprises a housing 11, composed of any material capableof protecting the shaped explosive charge from damage in handling. Thehousing material is preferably composed of a soft metal, such as lead orzinc, which gives increased confinement to the explosive detonation.Other materials have been employed in devices of this kind and it is notcontemplated that the nature of the housing material shall be limited.The housing 11 shown contains a centrally located ignition opening 12which is desirably equipped for service with a fuse of a suitablematerial, such as the well know Primacord fuse containing PETN(pentaerythrityl tetranitrate) or RDX (cyclotrimethylenetrinitramine)explosive. Communicating with the ignition opening 12, is an explosivebooster charge 13 positioned adjacent to the opening 12. Packed adjacentto the booster charge 13 within the confines of the housing 11 is themain shaped mass of explosive charge 14. The nature of the shapedexplosive charge may vary, but a detonating explosive which ispreferably of high density, such as a pressed or cast solid organicnitrate or nitro-compound, is generally suitable. Compressed PETN is onesuitable material and compressed or cast blends of PETN with TNT, forexample, in Similarly, RDX is a suitable explosive as are its highdensity mixtures with TNT, one suitable blend consisting of parts of RDXand 20 parts TNT. These explosive materials are suitable since theypossess high strength and upon detonation produce a high velocity,reaching maximum velocity -very rapidly. The booster charge 13 may becomposed of the same explosive as the main shaped charge or otherexplosives Well known to the art may be employed.

The foregoing components of the embodiment illustrated by FIG. 1 do notper se constitute essential features of the present invention. Theseforegoing components have been employed in one form or other in priorart devices designed to perforate borehole casings. An essential featurewhich permits accomplishing the objects of the invention is thecharacter of the concave metallic liner which seals off the open end ofthe housing 11 and the shaped explosive charge 14. As illustrated inFIG. 1, the concave liner 15 has a setolt 1.6 from the open end of thehousing 11. This setotf is frequently employed in devices of this typeto obtain the full benefits of the so-callecl Munroe effect.

The liner 15 in accordance with this invention is composed of a metal oralloy having a melting point low enough to substantially melt at thetemperatures produced by the compression caused when the shapedexplosive charge 14 is detonated. The specific temperature obtainedunder the conditions of compression resulting from detonation willdepend somewhat upon the specific metal or alloy of which the liner 15is composed. In general, however, it is contemplated that to obtain thebenefits of the invention, i.e., freedom from slugging or carroting, themetal or" which the liner is composed shall have a melting point of notmore than about 500 C. This melting point range is substantially lessthan the melting points of metals which have been employed in theconventional prior art devices of this type. Prior employed retals, suchas copper and steel, have melting points of about 1082 and 1539 (3.,respectively. The high melting points of these prior metals, beingvastly greater than those of the low melting metals and alloyscontemplated tor use in the liners of the present invention, prevent anysubstantial melting of the liner metal upon detonation of the shapedcharge. The difference in results obtained is illustrated by FIGS. 2 and3 of the drawings. FIG. 2 illustrates what happens in the penetrationhole produced when a liner of copper or steel is employed, whereas FIG.3 illustrates the penetration hole produced when a liner of metal oralloy melting below about 500 C. is employed. As shown in the twofigures, the earth formation is penetrated to form a hole 21. In thecase of FIG. 2, illustrating the use of a copper or steel liner, acarrot 22 is formed whereas no such carrot is formed in FIG. 3 employingthe liner of the present invention. The carrot 22 efi'ectively obstructsa substantial portion of a penetration hole as shown at 23.

It is desirable that the low melting metal or alloy comprising the liner15 have a tensile strength of between about 3,000 and 13,000 p.s.i. anda hardness of between about 5 and 22 on the Brinnel scale.

Although the liner 15 illustrated in FIG. 1 is in the form of a conehaving an angle (oz) of about 60, other angles such as between about and80 and other shapes may be employed. The difference in angle and shapeof the liner may be varied according to the dimensions of theperforation which one desires to produce. These variations are wellknown to those skilled in the art. Other shapes which may be employedinclude pyramidal, hemispherical, parabolic, etc.

Illustrative of the various metals and alloys which may be employed informing the concave liner are those disclosed by the examples whichfollow. It should be understood, however, that this is done solely byway of example and is intended neither to delineate the scope of theinvention nor limit the ambit of the appended claims. In the exampleswhich follow, and throughout the specification, the quantities of metalsare expressed in terms of percent by weight, unless otherwise specified.

EXAMPLES zinc-1.6% lead)melting (7) Leadantimony alloy lead-40%antimony)melting point, 270 C.

(8) Bismuth solder (40% bismuth, 40% lead, 20% tin)--melting point, 111C.

In addition to those specific metals and alloys disclosed in theforegoing examples, other low melting metals, and binary, ternary andquaternary alloys of bismuth, lead, tin, cadmium, indium, etc., may beemployed, provided the metal or alloy is capable of melting at thecompres sion temperatures reached upon detonating the shaped explosivecharge. it is characteristic of these metals and alloys to flow underhigh pressure or load which is related to their thermodynamic propertyof melting at a low temperature.

An additional important feature of the liner of the shaped charge of thepresent invention is its thickness. in prior apparatus of the presenttype, it has been considered necessary that to have a charge givingsatisfactory performance and penetration, the mass of the liner in frontof the shaped explosive charge must remain substantially constant frommetal to metal. Thus, for aluminum, a relatively low density metal, theliner must be relatively thick. For higher density metals, such ascopper and steel, it has been considered necessary that the liner bethinner. Thus, for an aluminum liner, having a specific gravity of 2.7,it has been considered necessary that the thickness of the liner be fromabout 2% to 6% of its diameter. For a steel liner, having a specificgravity of 7.85, it has been considered necessary that the linerthickness be from about 1 to 3% of the liner diameter. For copperliners, having a specific gravity of about 8.95, it is standard practicefor the thickness of the liner to be about 1.5% of the liner diameter.Following these standard teachings of the prior art, one wouldcontemplate that for a liner of lead, in accordance with the presentinvention, having a specific gravity of about 11.35, the thicknessshould be about 1% of the liner diameter. However, unexpectedly, we havediscovered that when the liner is composed of a low melting metal oralloy these teachings of the prior art regarding liner thickness havebeen found to produce unsatisfactory results. We have discovered that aliner of lead having a thickness of about 1% of the liner diameter doesnot provide satisfactory penetration. We have discovered that whenemploying the low melting metals, it is essential that the thickness ofthe liner must be much greater in relation to the density of the metalto provide satisfactory results. Thus, for example, in the case of alead liner in accordance with the present invention, it is necessarythat the liner thickness be from about 2% to 6%, with best results beingobtained at a thickness at about 4.0%. Thicknesses of the low meltingliners (in terms of percent thickness of liner diameter) compared withthe specific gravity of the metal is set forth in the diagram of FIG. 4of the accompanying drawing. As set forth in the diagram, the lowmelting point liners contemplated for use in the present inventionshould have a thickness expressed in terms of percent of the linerdiameter falling within the area delineated by the points ABCD. Optimumresults are obtained by values expressed by the line EF.

While we do not propose to be bound to any explanation as to how ourinvention succeeds in accomplishing its objects, we believe that whenemploying a low melting point metal liner it must be suflicientlymassive to prevent breakthrough of the explosion products until themetallic jet has had a chance to form. Good results are not obtainedwith liners which are too thick because the velocity of collapse is notsufliciently great. Thus, if the benefits and high penetrating power ofthe shaped explosive charge is to be obtained employing a low meltingmetallic liner, it is necessary that the liner be of a thickness withinthe range prescribed by the points ABCD of FIG. 4 of the drawings. Thisconcept of thickness of the liner applies only to the low melting pointmetallic liners of the invention.

Listed in the table below for each of the foregoing examples is thecorresponding specific gravity, desired liner thickness range andoptimum liner thickness value.

Table Thickness of liner Actual thickness for (percent of liner liner1.25 inches in Example Specific diameter) diameter N o. gravity DesiredOptimum Desired Optimum range value range value The value of theapparatus and liner of the invention is applicable to shaped charges foroil well penetration as distinguished from shaped charges intended formilitary purposes. Shaped charges intended for oil well penetration arecharacterized by having a shaped explosive charge distributed over alength which is less than two times its diameter.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:

*1. A well borehole casing perforating apparatus comprising a closedcontainer capable of being inserted into a well borehole comprising ahousing having an open end and containing a shaped high-order explosivecharge and a low melting metallic concave liner sealing the open end ofsaid housing, said low melting metallic concave liner being composed ofa metal having a melting point of not more than about 500 C., thesurface area of said liner in contact with said explosive charge beingsuch that said liner will disintegrate upon detonation of said explosivecharge, said liner having a thickness to diameter ratio within the areadelineated by the points ABCD of FIG. 4 of the attached drawings andwhich will produce a resulting perforation which is free from thepresence of a metallic slug.

2. A well borehole casing perforating apparatus comprising a closedcontainer capable of being inserted into a well borehole comprising ahousing having an open end and containing a shaped high-order explosivecharge and a low melting metallic concave liner sealing the open end ofsaid housing, said low melting metallic concave liner being comprised ofa metal having a melting point of not more than about 500 C., thesurface area of said liner in contact with said explosive charge beingsuch that said liner will disintegrate upon detonation of said explosivecharge, said liner having a thickness to diameter ratio which issubstantially that represented by the line EF of FIG. 4 of the attacheddrawings and which will produce a resulting perforation which is freefrom the presence of a metallic slug.

3. A well bore hole casing perforating apparatus comprising a closedcontainer capable of being inserted into a well borehole comprising ahousing having an open end and containing a shaped high-order explosivecharge and a low melting metallic concave liner sealing the open end ofsaid housing, said low melting metallic concave liner beingsubstantially lead, the surface area of said liner in contact with saidexplosive charge being such that said liner will distintegrate upondetonation of said explosive charge, said liner having a thickness todiameter ratio of about 4%.

References Cited in the file of this patent UNITED STATES PATENTS2,605,703 Lawson Aug. 5, 1952 2,667,836 Church et al Feb. 2, 1954FOREIGN PATENTS 693,164 Great Britain June 24, 1953 OTHER REFERENCESAmerican Institute of Mining and Metallurgical Engineers, TechnicalPublication No. 2158, Class A. Mining Technology, 1947, pages 1-13,Behavior of Metal Cavity Liners in Shaped Explosive Charges by George B.Clark and Walter H. Bruckner.

1.A WELL BOREHOLE CASING PERFORATING APPARATUS COMPRISING A CLOSEDCONTAINER CAPABLE OF BEING INSERTED INTO A WELL BOREHOLE COMPRISING AHOUSING HAVING AN OPEN END AND CONTAINING A SHAPED HIGH-ORDER EXPLOSIVECHARGE AND A LOW MELTING METALLIC CONCAVE LINER SEALING THE OPEN END OFSAID HOUSING, SAID LOW MELTING METALLIC CONCAVE LINER BEING COMPOSED OFA METAL HAVING A MELTING POINT OF NOT MORE THAN ABOUT 500*C., THESURFACE AREA OF SAID LINER IN CONTACT WITH SAID EXPLOSIVE CHARGE BEINGSUCH THAT SAID LINER WILL DISINTEGRATE UPON DETONATION OF SAID EXPLOSIVECHARGE, SAID LINER HAVING A THICKNESS TO DIAMETER RATIO WITHIN THE AREADELINEATED BY THE POINTS ABCD OF FIG. 4 OF THE ATTACHED DRAWINGS ANDWHICH WILL PRODUCE A RESULTING PERFORATION WHICH IS FREE FROM THEPRESENCE OF A METALLIC SLUG.